constraining the history of star formation of early type galaxies
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Constraining the History of Star Formation of Early-Type Galaxies. Ricardo Schiavon University of Virginia. Mini-Workshop, “Galaxy Mergers” STScI, October 4, 2006. Collaborators. Sandy Faber, Jenny Graves, David Koo, and the DEEP2 collaboration (Lick, UC Berkeley, Caltech, …)

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constraining the history of star formation of early type galaxies

Constraining the History of Star Formation of Early-Type Galaxies

Ricardo Schiavon

University of Virginia

Mini-Workshop, “Galaxy Mergers”

STScI, October 4, 2006

collaborators
Collaborators
  • Sandy Faber, Jenny Graves, David Koo, and the DEEP2 collaboration (Lick, UC Berkeley, Caltech, …)
  • Bob O’Connell, Bob Rood (Virginia), and Ruth Peterson (Lick)
  • Jim Rose (North Carolina), Nelson Caldwell (SAO), Stéphane Courteau (Queens), Lauren MacArthur (British Columbia)
  • Beatriz Barbuy, Paula Coelho (IAG/São Paulo), Bruno Castilho (LNA/Brazil)
motivation
Motivation
  • Ultimate Goal:Star formation histories of early-type (E – S0) galaxies
  • No CMDs: Integrated light
  • Stellar Population Synthesis => ages and abundances of stars

M49: A Giant Elliptical Galaxy

on an every week basis at astro ph

On an Every-week Basis at astro-ph

Cimatti et al. (2003)

Daddi et al. (2005)

abundance pattern
Abundance Pattern

Worthey et al. 92

Schiavon 2006

Stars in the Solar Neighborhood

Early-type Galaxies

The abundance patterns of early-type galaxies is not the same as that of the solar neighborhood => Enrichment by SNe II x SNe Ia

subtle differences
Subtle Differences

Stacked SDSS spectra from Eisenstein et al. (2003) - z ~ 0.15

[Fe/H]~0.15[Mg/H]~0.2 [C/H]~0.25 [N/H]~0.35

[Ca/H] ~ 0.25 Age ~ 2 Gyr

line index measurements the lick ids system

DEEP

Line Index Measurements: The Lick/IDS System

Comparison between measurements taken on Jones (1999) spectra and standard Lick/IDS measurements

the new lick system

DEEP

The “New” Lick System

Comparison between measurements taken on Jones (1999) spectra and those taken on FAST spectra (Schiavon et al. 2004)

Most of the scatter in the previous figure comes from Lick/IDS measurements

fitting functions

DEEP

Fitting Functions

Blue: [Fe/H] < -0.5

Green: -0.1 < [Fe/H] < -0.5

Red: [Fe/H] > -0.1

R.M.S. of fit: 0.2 Å (giants) and 0.4 Å (dwarfs)

Compare with 1.5 Å from Worthey & Ottaviani (1997), which is based on the same spectral library!

cluster integrated spectra

M67 & M32

Cluster Integrated Spectra

47 Tuc: Schiavon et al. (2002)

M 67: Schiavon et al. (2004)

Don’t believe what I tell you about galaxies if my models do not reproduce cluster data with the necessary accuracy, for the right input parameters

the models

M67 & M32

The Models

Schiavon (2006, ApJS, submitted)

http://www.astro.virginia.edu~/rps7v/Models/Models.html

  • Accurate line indices
  • Accurate stellar parameters
  • Abundance ratios from literature
  • Fitting functions (r.m.s. 1/3 of previous models)
  • Model predictions for SSPs
  • Comparison with cluster data (agreement within 0.1 dex in abundances of Fe,C,N,Mg,Ca, 1-2 Gyr in age)
  • New constraints on SFH of galaxies from comparison with SDSS data
sdss red early type galaxies

M67 & M32

SDSS Red Early-Type Galaxies

From Eisenstein et al. (2003)

abundance pattern1

M67 & M32

Abundance Pattern

[Fe/H]

[Mg/Fe]

[C/Fe]

[N/Fe]

[Ca/Fe]

Mean Age (Gyr)

Mr

Mr

sdss red early type galaxies1

M67 & M32

SDSS Red Early-Type Galaxies

From Eisenstein et al. (2003)

abundance pattern vs environment

M67 & M32

Abundance Pattern vs. Environment

High density

Intermediate density

Low density

Higher density environments are more N-rich

In the field, stars who live in brighter galaxies tend to be younger than those who live in their fainter counterparts

Mr

Mr

ages according to h

M67 & M32

Ages According to H

… are substantially younger than those based on Hß

the deep2 project

DEEP

The DEEP2 Project

Deep Extragalactic Evolutionary Probe

  • A survey of distant, faint galaxies with Keck/DEIMOS & HST
  • Goals: formation and evolution of galaxies and large scale structure
  • 60,000 galaxies, 0.7 < z < 1.4, R ~ 5,000
  • Complete down to R=24, ~ 4 square degrees in the sky
  • Large enough for robust comparison with local counterparts (e.g. SDSS, 2dF)
  • HST/ACS imaging
  • High spectral resolution: galaxy internal kinematics and stellar populations
the sample
The Sample

No morphologies!!

Color Cut

(U-B) > 0.25

Initial Sample

emission line cut
Emission-Line Cut

Contamination by late-types is ~ 15% (see Konidaris et al. 2005, in preparation)

results ages

M67 & M32

Results: Ages
  • Red galaxies at z~0.9 have undergone (small amounts of) recent star formation
  • Red galaxies at z~0.9 and z~0.1 are NOT connectetd by lines of passive evolution
results galaxies as a function of color

M67 & M32

Results: Galaxies as a function of Color
  • Young and metal-rich: 1.5 Gyr, solar [Fe/H]
  • Results are little sensitive to the choice of [α/Fe]
  • The color sequence seems to be a [Fe/H] sequence

Age

[Fe/H]

slide24

DEEP

Kelson et al. (2001): CLUSTER early-types evolve passively from a higher z of formation

conclusions

DEEP

Conclusions
  • We can estimate abundances of magnesium, carbon, nitrogen, and calcium, and they might be telling us new details about the history of star formation of early-type galaxies
  • Nitrogen abundances can be constraining the lower limit of the timescale for star formation in early-type galaxies. They are higher in denser environments. Why?
  • Can the strong abundance trends with galaxy mass be telling us something about how (un?) important dry merging is?
  • In the field, stars in giant galaxies seem to be younger, on average, than those in L* galaxies. Interesting result, but beware of H emission-line infill.
conclusions1

DEEP

Conclusions
  • On the basis of accurate models and data, one is able to detect 2nd order effects on Balmer lines
  • This detection allows one to constrain the age spread of stars in red galaxies, revealing the presence of small amounts of young stars and indicating a prolonged history of star formation
  • Analysis of DEEP2 and SDSS data suggests an extended history of star formation for field red galaxies
  • The fact that [Mg/Fe] is enhanced may be telling us that mass fraction in the young component today is very small
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